Hydrocarbons often are utilized as fuels and/or as chemical feedstocks for manufacturing industries. Hydrocarbons naturally may be present within subterranean formations, which also may be referred to herein as reservoirs and/or as hydrocarbon reservoirs. Such hydrocarbons may occur in a variety of forms, which broadly may be categorized herein as conventional hydrocarbons and unconventional hydrocarbons. A process utilized to remove a given hydrocarbon from a corresponding subterranean formation may be selected based upon one or more properties of the hydrocarbon and/or of the subterranean formation.
As an example, conventional hydrocarbons generally have a relatively lower viscosity and extend within relatively higher fluid permeability subterranean formations. As such, these conventional hydrocarbons may be pumped from the subterranean formation utilizing a conventional oil well.
As another example, unconventional hydrocarbons generally have a relatively higher viscosity and/or extend within relatively lower fluid permeability subterranean formations. As such, a conventional oil well may be ineffective at producing unconventional hydrocarbons. Instead, unconventional hydrocarbon production techniques may be utilized.
Examples of unconventional hydrocarbon production techniques that may be utilized to produce viscous hydrocarbons from a subterranean formation include thermal recovery processes. Thermal recovery processes generally inject a thermal recovery stream, at an elevated temperature, into the subterranean formation. The thermal recovery stream contacts the viscous hydrocarbons, within the subterranean formation, and heats, dissolves, and/or dilutes the viscous hydrocarbons, thereby generating mobilized viscous hydrocarbons. The mobilized viscous hydrocarbons generally have a lower viscosity than a viscosity of the naturally occurring viscous hydrocarbons at the native temperature and pressure of the subterranean formation and may be pumped and/or flowed from the subterranean formation. A variety of different thermal recovery processes have been utilized, including cyclic steam stimulation processes, solvent-assisted cyclic steam stimulation processes, steam flooding processes, solvent-assisted steam flooding processes, steam-assisted gravity drainage processes, solvent-assisted steam-assisted gravity drainage processes, heated vapor extraction processes, liquid addition to steam to enhance recovery processes, and/or near-azeotropic gravity drainage processes.
Thermal recovery processes may differ in the mode of operation and/or in the composition of the thermal recovery stream. However, all thermal recovery processes rely on injection of the thermal recovery stream into the subterranean formation at the elevated temperature, and thermal contact between the thermal recovery stream and the subterranean formation heats the subterranean formation. Thus, and after performing a given thermal recovery process within a given subterranean formation, a significant amount of thermal energy may be stored within the subterranean formation, and it may be costly to maintain the temperature of the subterranean formation and/or to heat the thermal recovery stream prior to injection of the thermal recovery stream within the subterranean formation.
In addition, as the viscous hydrocarbons are produced from the subterranean formation, an amount of energy required to produce viscous hydrocarbons increases due to increased heat loss within the subterranean formation. Similarly, a ratio of a volume of the thermal recovery stream provided to the subterranean formation to a volume of mobilized viscous hydrocarbons produced from the subterranean formation also increases. Both of these factors decrease economic viability of thermal recovery processes late in the life of a hydrocarbon well and/or after production and recovery of a significant fraction of the original oil-in-place from a given subterranean formation. Thus, there exists a need for improved methods of recovering viscous hydrocarbons from a subterranean formation.